Maskasky U.S. Pat. No. 5,292,632 reported the discovery of high chloride {100} tabular grain emulsions. Maskasky reports no emulsion preparations in which the high chloride {100} tabular grains have a thickness of 0.1 .mu.m or less. The thinnest tabular grain emulsion set out in the Maskasky examples has a thickness already increased to 0.115 .mu.m at a mean grain ECD of only 1.28 .mu.m. In the only two examples provided by Maskasky that show mean ECD's of 2.0 .mu.m or more, the emulsion with a mean tabular grain ECD of 2.18 .mu.m exhibits a mean thickness of 0.199 .mu.m while the emulsion with a mean ECD of 2.20 .mu.m exhibits a mean thickness of 0.23 .mu.m. The high chloride {100} tabular grains of Maskasky were obtained by adsorbing a grain growth modifier to the surfaces of the grains.
House et al U.S. Pat. No. 5,320,938, relying on iodide introduced during grain nucleation to promote high chloride {100} tabular grain growth, discloses as its thinnest tabular grain example an emulsion having in a selected tabular grain popular a mean grain thickness of 0.033 .mu.m, but with an ECD of only 0.54 .mu.m. In the only two examples provided by House et al that show mean ECD's of 2.0 .mu.m or more, the emulsion with a mean tabular grain ECD of 2.28 .mu.m exhibits a mean thickness of 0.195 .mu.m while the emulsion with a mean ECD of 2.55 .mu.m exhibits a mean thickness of 0.165 .mu.m.
Brust et al U.S. Pat. No. 5,314,798, an improvement on House et al that adds a higher iodide band to improve emulsion sensitivity, provides no example of a high chloride {100} tabular grain emulsion having a mean grain thickness of 0.1 .mu.m or less. The largest mean ECD high chloride {100} tabular grain emulsion included in the Brust et al examples exhibits a mean ECD of 2.1 .mu.m and a mean thickness of 0.16 .mu.m.
Chang et al U.S. Pat. No. 5,413,904 discloses an improvement on the precipitation process of House et al wherein iodide introduction is delayed until after grain nucleation as a technique for increasing the percentage of total grain projected area accounted for by high chloride {100} tabular grains. Chang et al reports a tabular grain emulsion having a mean ECD of only 1.04 .mu.m having very thin (0.07 .mu.m) grains; however, the thicknesses of the example emulsions having a mean ECD of at least 2.0 .mu.m ranged from 0.14 to 0.25 .mu.m.